1. Field of the Invention
The present invention relates generally to magnetic tape heads, and more specifically to a multi-track longitudinal tape head having a unique metal-in-gap configuration to increase gap-field strength.
2. Related Art
Magnetic tape drives are commonplace in today's computer industry. These tape drives are used to store digital information onto magnetic tapes and to subsequently read the stored information. Two examples of a magnetic tape drive are the IBM 3480 tape drive available from International Business Machines in Armonk, N.Y., and the StorageTek 4480 tape drive available from Storage Technology Corporation in Louisville, Colo.
Magnetic tapes are typically available in two formats: the cassette and the cartridge. The cassette tape is a two-reel mechanism that includes a supply reel and a take-up reel. Cassette tape drives thread the magnetic tape along a transport path, past one or more magnetic transducer heads, and then transport the tape such that it travels along the transport path. The tape is taken from the supply reel and wound onto the take-up reel.
For cartridge tapes, the take-up reel is external to the tape cartridge and typically provided internal to the tape drive. When a cartridge is inserted into a tape drive, it is threaded along the transport path by the tape drive and fastened to the take-up reel.
Writing data to and reading data from the magnetic tapes is accomplished using a tape head. For data operations, tape heads are typically multi-track heads capable of reading and writing several streams of data (one per track) simultaneously.
A typical tape head assembly for a digital magnetic tape drive comprises an approximately horseshoe-shaped core made from a magnetic material such as ferrite. A coil of wire wound around the core is used to induce a magnetic field within the core. The open end of the horseshoe forms what is referred to as a gap. Often times, the tape head manufacturing process leaves a slot at the opposite end of the horseshoe. This slot is known as a "back gap" and has a comparatively low magnetic reluctance to the flux lines through the core.
For write operations, a time-varying electric current is sent through the coil. This current is referred to as "write current." This write current produces a time-varying magnetic field in the core. If the core was a complete circle (e.g., a toroid) the magnetic flux lines would travel in a circle along the core. Because the core is not a complete circle but has a gap, the flux lines bridge this gap and create a "gap field."
The magnetic tape is passed over the gap at a predetermined distance such that the magnetic surface of the tape passes through a fringing field from the gap. As the write current changes, the field at the gap changes in intensity and direction. These temporal variations in gap field result in a spatial pattern of magnetization on the magnetic tape. Thus, electronic data signals can be converted to magnetic signals and the data stored magnetically on the magnetic tape.
To improve the quality of recordings, the audio and video industries have begun using high coercivity tapes. These tapes have a high residual flux density, B.sub.r, and require a high coercive force, H.sub.c, to write data to the tape. An example of such a tape is a metal-particle magnetic tape on which metal magnetic powder is coated on a non-magnetic substrate, wherein the metal powder forms a thin magnetic layer.
To write information to a high coercivity tape, such as a metal-particle tape, the strength of the magnetic field at the write gap must be sufficient to overcome the high coercivity of the tape. The gap field needed is typically greater than that which can be generated using conventional ferrite heads. With conventional ferrite heads, the gap field strength is substantially proportional to the write current, but only up to a threshold level where the magnetic material on either side of the frontgap (the pole tip) saturates. After this saturation point is reached, increases in write current lead to little or no increase in the gap field strength. This phenomenon is known as "pole-tip saturation."
Conventional videotape heads have been developed for writing to high coercivity tapes. These tape heads are manufactured by forming a magnetic alloy with a high saturation magnetic flux density B.sub.s, such as Sendust, on a non-magnetic or magnetic core half. The presence of the high B.sub.s material on either or both sides of the front gap allows the video tape head to write to high coercivity tapes while avoiding the problem of pole tip saturation. The layer of Sendust is typically formed using vapor deposition techniques such as sputtering. An example of such a conventional tape head is illustrated in FIG. 1. The major portion of this head is formed of glass or a like non-magnetic material 102, 104 and a magnetic film 106. Magnetic film 106 is of a thickness equal to the track width formed therebetween. Magnetic film 106 is typically a high B.sub.s alloy such as Sendust.
Conventional tape heads such as the one illustrated in FIG. 1, are commonly used with audio and video tape recorders. This and additional tape head configurations using different configurations of high B.sub.s alloys are described in U.S. Pat. No. 4,755,899 to Kobayashi, et al., which is incorporated herein by reference.
The use of high coercivity tapes has been primarily confined to the audio and video industries. Currently, high coercivity tapes are also being used by data storage systems with tape transports and tape heads similar to those used in the video industry. High B.sub.s alloys, such as Sendust, do not appear to have been used in multi-track longitudinal tape heads used for data storage.
A conventional multi-track longitudinal tape head module 200 is illustrated in FIG. 2. Referring now to FIG. 2, an alternating pattern of read and write tracks is formed by providing an alternating pattern of write closure poles 202 (referred to as write poles 202) and read closure poles 206 (referred to as read poles 206) opposite a block of substrate material 208 and separated by a gap 204. A write coil is present on substrate material 208 opposite write pole 202. A read device, such as a magneto-resistive sensor, is present on substrate material 208 opposite read pole 206. Write poles 202 and read poles 206 are embedded in a non-magnetic glass matrix insulator 210. The glass insulator 210 between write poles 202 and read poles 206 acts as a track isolator. Material 212, provided for structural purposes, can be either magnetic or non-magnetic material.
For read and write operations in two tape directions, two such modules 200 are provided adjacent to one another. An example of this conventional bi-directional, read-write tape head is illustrated in FIG. 1 of U.S. Pat. No. 5,065,483 to Zammit. U.S. Pat. No. 5,065,483 is incorporated herein by reference.
Another conventional design for a multi-track longitudinal tape head is exemplified by the IBM 3480 and StorageTek 4480 18-track non interleaved tape heads. In this design, a first module is provided which comprises write closure poles opposite a first substrate with write coils. A second module is provided which comprises a solid block of ferrite opposite a second substrate with magneto-resistive sensors. The first and second modules are configured adjacent to one another to provide a unidirectional read-after-write tapehead.
The magnetic tape travels across a front face of the tape head perpendicular to gap 204 in the directions illustrated by arrow 242. The top face, the face across which the magnetic tape travels, is typically convex. During read and write operations, the tape is usually separated from the top face of the tape head by a thin layer of air.
Apparently, in conventional multi-track, longitudinal magnetic tape heads, write poles 202, and substrate 208 are made entirely of nickel-zinc-ferrite, or manganese-zinc-ferrite. As a result, the gap field strength of these conventional heads is not sufficient to write data to high coercivity tapes.
What is needed is a longitudinal multi-track tape head capable of writing data to high coercivity magnetic tapes without the problem of pole-tip saturation.